Myeloproliferative disorders (MPDs) are characterized by cytokine hypersensitivity and apoptosis resistance. Development of a block in myeloid differentiation is associated with progression of MPD to acute myeloid leukemia (AML) and portends poor prognosis. Identifying molecular markers of this transition may suggest targets for therapeutic intervention. Interferon consensus sequence binding protein (ICSBP, also known as IRF8) is an interferon-regulatory transcription factor that functions as a leukemia tumor suppressor. In mice, ICSBP deficiency induces an MPD that progresses to AML over time, suggesting that ICSBP deficiency is sufficient for myeloproliferation, but additional genetic lesions are necessary for AML. Since activity of ICSBP is influenced by tyrosine phosphorylation state, we hypothesized that mutations in molecular pathways that regulate this process might synergize with ICSBP deficiency for progression to AML. Consistent with this, we found that constitutive activation of SHP2 protein tyrosine phosphatase synergized with ICSBP haploinsufficiency to facilitate cytokine-induced myeloproliferation, apoptosis resistance, and rapid progression to AML in a murine bone marrow transplantation model. Constitutive SHP2 activation cooperated with ICSBP deficiency to increase the number of progenitors in the bone marrow and myeloid blasts in circulation, indicating a block in differentiation. Since SHP2 activation and ICSBP deficiency may coexist in human myeloid malignancies, our studies have identified a molecular mechanism potentially involved in disease progression in such diseases.
Iwona Konieczna, Elizabeth Horvath, Hao Wang, Stephan Lindsey, Gurveen Saberwal, Ling Bei, Weiqi Huang, Leonidas Platanias, Elizabeth A. Eklund
The proliferation and differentiation of hematopoietic stem cells (HSCs) is finely regulated by extrinsic and intrinsic factors via various signaling pathways. Here we have shown that, similar to mice deficient in the lipid phosphatase SHIP, loss of 2 Src family kinases, Lyn and Hck, profoundly affects HSC differentiation, producing hematopoietic progenitors with increased proliferation, reduced apoptosis, growth factor–independent survival, and skewed differentiation toward M2 macrophages. This phenotype culminates in a Stat5-dependent myeloproliferative disease that is accompanied by M2 macrophage infiltration of the lung. Expression of a membrane-bound form of SHIP in HSCs lacking both Lyn and Hck restored normal hematopoiesis and prevented myeloproliferation. In vitro and in vivo studies suggested the involvement of autocrine and/or paracrine production of IL-3 and GM-CSF in the increased proliferation and myeloid differentiation of HSCs. Thus, this study has defined a myeloproliferative transformation-sensitive signaling pathway, composed of Lyn/Hck, SHIP, autocrine/paracrine cytokines, and Stat5, that regulates HSC differentiation and M2 macrophage programming.
Wenbin Xiao, Hong Hong, Yuko Kawakami, Clifford A. Lowell, Toshiaki Kawakami
Many patients with anemia fail to respond to treatment with erythropoietin (Epo), a commonly used hormone that stimulates erythroid progenitor production and maturation by human BM or by murine spleen. The protein product of growth arrest–specific gene 6 (Gas6) is important for cell survival across several cell types, but its precise physiological role remains largely enigmatic. Here, we report that murine erythroblasts released Gas6 in response to Epo and that Gas6 enhanced Epo receptor signaling by activating the serine-threonine kinase Akt in these cells. In the absence of Gas6, erythroid progenitors and erythroblasts were hyporesponsive to the survival activity of Epo and failed to restore hematocrit levels in response to anemia. In addition, Gas6 may influence erythropoiesis via paracrine erythroblast-independent mechanisms involving macrophages. When mice with acute anemia were treated with Gas6, the protein normalized hematocrit levels without causing undesired erythrocytosis. In a transgenic mouse model of chronic anemia caused by insufficient Epo production, Gas6 synergized with Epo in restoring hematocrit levels. These findings may have implications for the treatment of patients with anemia who fail to adequately respond to Epo.
Anne Angelillo-Scherrer, Laurent Burnier, Diether Lambrechts, Richard J. Fish, Marc Tjwa, Stéphane Plaisance, Rocco Sugamele, Maria DeMol, Eduardo Martinez-Soria, Patrick H. Maxwell, Greg Lemke, Stephen P. Goff, Glenn K. Matsushima, H. Shelton Earp, Marc Chanson, Désiré Collen, Shozo Izui, Marc Schapira, Edward M. Conway, Peter Carmeliet
Phosphatidylinositol-4,5-bisphosphate (PIP2) is an abundant phospholipid that contributes to second messenger formation and has also been shown to contribute to the regulation of cytoskeletal dynamics in all eukaryotic cells. Although the α, β, and γ isoforms of phosphatidylinositol-4-phosphate-5-kinase I (PIP5KI) all synthesize PIP2, mammalian cells usually contain more than one PIP5KI isoform. This raises the question of whether different isoforms of PIP5KI fulfill different functions. Given the speculated role of PIP2 in platelet and megakaryocyte actin dynamics, we analyzed murine megakaryocytes lacking individual PIP5KI isoforms. PIP5KIγ–/– megakaryocytes exhibited plasma membrane blebbing accompanied by a decreased association of the membrane with the cytoskeleton. This membrane defect was rescued by adding back wild-type PIP5KIγ, but not by adding a catalytically inactive mutant or a splice variant lacking the talin-binding motif. Notably, both PIP5KIβ- and PIP5KIγ–/– cells had impaired PIP2 synthesis. However, PIP5KIβ-null cells lacked the membrane-cytoskeleton defect. Furthermore, overexpressing PIP5KIβ in PIP5KIγ–/– cells failed to revert this defect. Megakaryocytes lacking the PIP5KIγ-binding partner, talin1, mimicked the membrane-cytoskeleton defect phenotype seen in PIP5KIγ–/– cells. These findings demonstrate a unique role for PIP5KIγ in the anchoring of the cell membrane to the cytoskeleton in megakaryocytes, probably through a pathway involving talin. These observations further demonstrate that individual PIP5KI isoforms fulfill distinct functions within cells.
Yanfeng Wang, Rustem I. Litvinov, Xinsheng Chen, Tami L. Bach, Lurong Lian, Brian G. Petrich, Susan J. Monkley, David R. Critchley, Takehiko Sasaki, Morris J. Birnbaum, John W. Weisel, John Hartwig, Charles S. Abrams
Yanfeng Wang, Rustem I. Litvinov, Xinsheng Chen, Tami L. Bach, Lurong Lian, Brian G. Petrich, Susan J. Monkley, Yasunori Kanaho, David R. Critchley, Takehiko Sasaki, Morris J. Birnbaum, John W. Weisel, John Hartwig, Charles S. Abrams
Sickle-cell disease (SCD) and β thalassemia constitute worldwide public health problems. New therapies, including hydroxyurea, have attempted to augment the synthesis of fetal hemoglobin (HbF) and improve current treatment. Lenalidomide and pomalidomide are members of a class of immunomodulators used as anticancer agents. Because clinical trials have demonstrated that lenalidomide reduces or eliminates the need for transfusions in some patients with disrupted blood cell production, we investigated the effects of lenalidomide and pomalidomide on erythropoiesis and hemoglobin synthesis. We used an in vitro erythropoiesis model derived from human CD34+ progenitor cells from normal and SCD donors. We found that both compounds slowed erythroid maturation, increased proliferation of immature erythroid cells, and regulated hemoglobin transcription, resulting in potent induction of HbF without the cytotoxicity associated with other HbF inducers. When combined with hydroxyurea, pomalidomide and, to a lesser extent, lenalidomide were found to have synergistic effects on HbF upregulation. Our results elucidate what we believe to be a new mechanism of action of pomalidomide and lenalidomide and support the hypothesis that pomalidomide, used alone or in combination with hydroxyurea, may improve erythropoiesis and increase the ratio of fetal to adult hemoglobin. These findings support the evaluation of pomalidomide as an innovative new therapy for β-hemoglobinopathies.
Laure A. Moutouh-de Parseval, Dominique Verhelle, Emilia Glezer, Kristen Jensen-Pergakes, Gregory D. Ferguson, Laura G. Corral, Christopher L. Morris, George Muller, Helen Brady, Kyle Chan
Thrombocytosis is associated with inflammation, and certain inflammatory cytokines, including IFN-γ, stimulate megakaryocyte and platelet production. However, the roles of IFN-γ and its downstream effector STAT1 in megakaryocyte development are poorly understood. We previously reported that STAT1 expression was significantly downregulated in Gata1-knockdown murine megakaryocytes, which also have impaired terminal maturation. Here, we show that ectopic expression of STAT1, or its target effector IRF-1, rescued multiple defects in Gata1-deficient megakaryopoiesis in mice, inducing polyploidization and expression of a subset of platelet-expressing genes. Enforced expression of STAT1, IRF-1, or GATA-1 enhanced phosphorylation of STAT1, STAT3, and STAT5 in cultured Gata1-deficient murine megakaryocytes, with concomitant megakaryocyte maturation. In contrast, enhanced thrombopoietin signaling, conferred by enforced expression of constitutively active JAK2 or c-MPL, induced phosphorylation of STAT3 and STAT5, but not STAT1, and failed to rescue megakaryocyte maturation. Finally, megakaryocytes from Stat1–/– mice were defective in polyploidization. Together, these findings reveal a unique role for STAT1 in megakaryopoiesis and provide new insights into how GATA-1 regulates this process. Our studies elucidate potential mechanisms by which various inflammatory disorders can cause elevated platelet counts.
Zan Huang, Terri D. Richmond, Andrew G. Muntean, Dwayne L. Barber, Mitchell J. Weiss, John D. Crispino
Transgenic expression of the abnormal products of acute myeloid leukemia–associated (AML-associated) primary chromosomal translocations in hematopoietic stem/progenitor cells initiates leukemogenesis in mice, yet additional mutations are needed for leukemia development. We report here aberrant expression of PR domain containing 16 (PRDM16) in AML cells with either translocations of 1p36 or normal karyotype. These carried, respectively, relatively high prevalence of mutations in the TP53 tumor suppressor gene and in the nucleophosmin (NPM) gene, which regulates p53. Two protein isoforms are expressed from PRDM16, which differ in the presence or absence of the PR domain. Overexpression of the short isoform, sPRDM16, in mouse bone marrow induced AML with full penetrance, but only in the absence of p53. The mouse leukemias were characterized by multilineage cellular abnormalities and megakaryocyte dysplasia, a common feature of human AMLs with 1p36 translocations or NPM mutations. Overexpression of sPRDM16 increased the pool of HSCs in vivo, and in vitro blocked myeloid differentiation and prolonged progenitor life span. Loss of p53 augmented the effects of sPRDM16 on stem cell number and induced immortalization of progenitors. Thus, overexpression of sPRDM16 induces abnormal growth of stem cells and progenitors and cooperates with disruption of the p53 pathway in the induction of myeloid leukemia.
Danielle C. Shing, Maurizio Trubia, Francesco Marchesi, Enrico Radaelli, Elena Belloni, Cinzia Tapinassi, Eugenio Scanziani, Cristina Mecucci, Barbara Crescenzi, Idoya Lahortiga, Maria D. Odero, Giuseppe Zardo, Alicja Gruszka, Saverio Minucci, Pier Paolo Di Fiore, Pier Giuseppe Pelicci
Bile salt–dependent lipase (BSDL) is an enzyme involved in the duodenal hydrolysis and absorption of cholesteryl esters. Although some BSDL is transported to blood, the role of circulating BSDL is unknown. Here, we demonstrate that BSDL is stored in platelets and released upon platelet activation. Because BSDL contains a region that is structurally homologous to the V3 loop of HIV-1, which binds to CXC chemokine receptor 4 (CXCR4), we hypothesized that BSDL might bind to CXCR4 present on platelets. In human platelets in vitro, both BSDL and a peptide corresponding to its V3-like loop induced calcium mobilization and enhanced thrombin-mediated platelet aggregation, spreading, and activated αIIbβ3 levels. These effects were abolished by CXCR4 inhibition. BSDL also increased the production of prostacyclin by human endothelial cells. In a mouse thrombosis model, BSDL accumulated at sites of vessel wall injury. When CXCR4 was antagonized, the accumulation of BSDL was inhibited and thrombus size was reduced. In BSDL–/– mice, calcium mobilization in platelets and thrombus formation were attenuated and tail bleeding times were increased in comparison with those of wild-type mice. We conclude that BSDL plays a role in optimal platelet activation and thrombus formation by interacting with CXCR4 on platelets.
Laurence Panicot-Dubois, Grace M. Thomas, Barbara C. Furie, Bruce Furie, Dominique Lombardo, Christophe Dubois
The R200W mutation in the von Hippel–Lindau (VHL) tumor suppressor protein (pVHL) is unique in that it is not associated with tumor development, but rather with Chuvash polycythemia, a heritable disease characterized by elevated hematocrit and increased serum levels of erythropoietin and VEGF. Previous studies have implicated hypoxia-inducible factor–1α (HIF-1α) signaling in this disorder, although the effects of this mutation on pVHL function are not fully understood. In order to explore the mechanisms underlying the development of this polycythemia, we generated mice homozygous for the R200W mutation (VhlR/R). VhlR/R mice developed polycythemia highly similar to the human disease. The activity of HIF proteins, specifically the HIF-2α isoform, was upregulated in ES cells and tissues from VhlR/R mice. Furthermore, we observed a striking phenotype in VhlR/R spleens, with greater numbers of erythroid progenitors and megakaryocytes and increased erythroid differentiation of VhlR/R splenic cells in vitro. These findings suggest that enhanced expression of key HIF-2α genes promotes splenic erythropoiesis, resulting in the development of polycythemia in VhlR/R mice. This mouse model is a faithful recapitulation of this VHL-associated syndrome and represents a useful tool for studying polycythemias and investigating potential therapeutics.
Michele M. Hickey, Jennifer C. Lam, Natalie A. Bezman, W. Kimryn Rathmell, M. Celeste Simon